In recent years, advances in regenerative medicine have inspired therapies targeted at the cellular level. These therapies seek to implant cells or cellular clusters, manipulate cellular pathways, and target the delivery of drugs. For example, a wide range of cell lines have been enclosed within semipermeable and biocompatible immobilization devices that control the bidirectional diffusion of molecules and cell release (R. P. Lanza, J. L. Hayes, W. L. Chick, Nat. Biotechnol. 14, 1107 (1996); G. Drive, R. M. Hernandez, A. R. Gascon, M. Igartua, J. L. Pedraz, J. L., Trends in Biotechnol. 20, 382 (2002); N. E. Simpson, S. C. Grant, S. J. Blackband, I. Constantinidis, Biomaterials 24, 4941 (2003)). Concurrent advances in microtechnology have revolutionized medicine, as new implantable devices, microarrays, biocapsules and microprobes are developed. These devices have facilitated cellular encapsulation, on-demand drug release, and early diagnosis of diseases (J. T. Santini, M. J. Cima, R. Langer, Nature 397, 335 (1999); J. Kost, R. Langer, Adv. Drug Delivery Rev. 6, 19 (1991); L. Leoni, T. A. Desai, Adv. Drug Delivery Rev. 56, 211 (2004); B. Ziaie, A. Baldi. M. Lei, Y. Gu, R. A. Siegel, Adv. Drug Delivery Rev. 56, 145 (2004); T. A. Desai, T. West, M. Cohen, T. Boiarski, A. Rampersaud, Adv. Drug Delivery Rev. 56, 1661 (2004); J. T. Santini, A. C. Richards, R. Scheidt, M. J. Cima, R. Langer, Angew. Chem. 39, 2396 (2000); Z. Fireman, E. Mahajna, E. Broide, M. Shapiro, L. Fich, A. Sternberg, Y. Kopelman, E. Scapa, Gut 52, 390 (2003)). In contrast to polymeric, hydrogel, and sol-gel based processes that have been used for encapsulation and delivery, conventional silicon (Si) based microfabrication has high reproducibility, provides mechanical and chemical stability, and allows the incorporation of electronic and optical modules within the device, thereby facilitating wireless telemetry, remote activation and communication, in vivo. However, Si based microfabrication is inherently a two dimensional (2D) process and it is extremely difficult to fabricate three-dimensional (3D) systems using conventional microfabrication (M. Madou, Fundamentals of Microfabrication (CRC, Boca Raton, Fla., 1997)). A 3D medical device has several advantages over its 2D counterpart: (a) a larger external surface area to volume ratio, thereby maximizing interactions with the surrounding medium, and providing space to mount different diagnostic or delivery modules, (b) a finite volume allowing encapsulation of cells and drugs, and (c) a geometry that reduces the chances of the device being undesirably lodged in the body.
In one aspect of the present invention, biocontainers (i.e., boxes, hollow particles) have been fabricated by a strategy that combines the advantages of three-dimensionality with the desirable aspects of Si-based microfabrication to facilitate the delivery of therapeutic agents in situ. For example, the containers are loaded with microbeads or cells embedded in a gel, and thus can be used either in conjunction with present day immobilization systems used in cell encapsulation technology, or they can be used independently. In another aspect, the biocontainers also can be used for encapsulation of functional cells within the porous containers for in vitro and in vivo release of therapeutic agents with or without immunosuppression. For example, the containers can be used for encapsulation and delivery of insulin secreting cells for implantation in patients with diabetes, for placing tumor innocula in animal models where constraining cells within a small region is necessary, and for delivery of functional neuronal PC12 cells. In some embodiments, the faces of the container are patterned with microscale perforations, allowing control over perfusion and release of its contents with the surrounding medium. The advantageous attributes of the containers are a parallel fabrication process with versatility in sizes and shapes; precise and monodisperse surface porosity; and the ability for remote guidance using magnetic fields. In another aspect, the containers of the present invention are easily detected and non-invasively tracked using conventional magnetic resonance imaging (MRI) and do not require the presence of a contrast agent.